Re: [PATCH 5/5] virtio: make virtqueue_add_buf() returning 0 on success, not capacity.

Note: I also have minor cleanups to virtio drivers to change (ret >= 0)
to (ret == 0) where it would otherwise be confusing for new readers, but
I didn't clutter the list with them.  See my virtio-wip tree for the
gory details.

Cheers,
Rusty.